The present invention relates to mobile telephone and related wireless communications systems, and, particularly, to a novel and improved method for controlling transmitter power in code division multiple access (CDMA) mobile terminals.
Wireless communications systems, such as cellular telephone systems, generally require at least one mobile terminal and any number of base stations to provide full duplex communications between the mobile terminal and the base station providing the best communication path. Typical mobile communications are accomplished using CDMA spread-spectrum communication signals. Such techniques allow the frequency spectrum to handle multiple transmissions, thereby significantly increasing communication capacity. In CDMA systems, proper control of transmitter power for each mobile terminal is required to reduce interference with other users and further increase system capacity.
During operation, the distance between a mobile terminal and a base station may constantly change, and the particular base station through which communications are facilitated may also change. Furthermore, ground-based mobile communications systems are subject to signal propagation losses due to interference from other communications systems, changes in landscape, and physical structures. Given the constantly changing and unpredictable environment in which communications are provided, a mobile terminal must constantly control its transmit power to ensure sufficient signal strength to transmit signals to the base station as well as minimize interference with other systems and communication channels.
Mobile terminals generally control their transmit power based on power control commands received from the base station and the strength of signals received from the base station. Additional background information is provided in U.S. Pat. No. 5,056,109 entitled METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM, the disclosure of which is incorporated herein by reference.
As noted, transmit power is typically controlled using commands from the base station and the strength of the received signals via gain signals provided to one or more variable gain amplifiers operating in the terminal""s intermediate frequency (IF). The commands from the base station are generally processed by the mobile terminal""s receiving circuitry and control system and typically provide a method of fine tuning the terminal""s transmit power level. Control based on received signal strength typically provides a method of coarse tuning the terminal""s transmit power level.
Typically, a mobile terminal has an automatic gain control (AGC) detector configured to provide a gain control signal based on the signal strength of received signals. The gain control signal is also provided to a variable gain amplifier operating in the intermediate frequency. Generally, both of these gain control signals are provided in analog form to a single variable gain amplifier with multiple gain controls or separate amplifiers having a single gain control. U.S. Pat. No. 5,056,109, mentioned above, provides a system configured with dual variable gain amplifiers, both operating in the IF range under analog control.
Currently, mobile terminals have relatively large power control requirements necessitating precise control throughout a wide range of operation. These terminals provide more and more processing ability in smaller packages. As the terminals become smaller, provide more processing power, and are required to operate over widely varying power levels, isolating highly sensitive gain control signals from noise and other signal components stemming from analog and digital circuitry becomes more difficult. As the terminals continue to decrease in size, and the terminal""s electronics become more integrated, design techniques of the prior art will have difficulty achieving precise control over wide operating ranges. Furthermore, providing a single integrated circuit solution for a terminal""s transmitter electronics would be difficult to implement.
Thus, there is a need for an improved transmission power control technique for mobile terminals. There is a need to provide greater isolation of gain control signals from the ever-increasing number of digital and analog signals present in telephone electronics and integrated circuits, as well as a need to decrease the sensitivity of gain control signals for the various variable gain amplifiers in these systems.
Power control circuitry of the present invention cooperates with the transmitting section of a mobile terminal to provide gain control for variable gain amplifiers operating on signals of different frequencies. Preferably, one variable gain amplifier controls the gain of signals in the signal transmission path in the IF section and another variable gain amplifier controls gain in the signal transmission path in the radio frequency (RF) section. One variable gain amplifier may be controlled based on the strength of the received signals while the other may be controlled based on commands from the base station. In addition, one or both of the amplifiers may optionally be controlled in whole or in part based on calibration and/or alignment settings established during manufacturing. Preferably, the gain control signal based on received signal strength is a pure digital signal substantially immune to noise and the control signal received from the control system is analog based. Amplifiers receiving the digital control signal are configured to provide a corresponding amplifier gain.
These and other aspects of the present invention will become apparent to those skilled in the art after reading the following description of the preferred embodiments when considered with the drawings.